Author(s): LU, Q., CHEN, M., WANG, J., ZHAO, Y., GUO, X., GU, F., JIANG, Y., DONG, B., Institution: PEKING UNION MEDICAL COLLEGE, Country: CHINA, Abstract-ID: 228

INTRODUCTION:
Adolescent obesity and depressive symptoms have risen concurrently, often co-occurring and increasing disease burden. Physical activity (PA) and diet are key modifiable factors but evidence integrating PA temporal distribution and adherence to the planetary health diet (PHDI-green) in relation to multimorbidity remains limited, particularly regarding sex differences. This study examined sex-specific associations of PA and PHDI-green adherence with obesity, depressive symptoms and multimorbidity.
METHODS:
From 2022 to 2024, a stratified cluster random sample of adolescents aged 11–18 years was selected in Zhejiang Province. PA and dietary behaviors were assessed through standardized questionnaires. PHDI-green, defined as daily consumption of both fruits and vegetables with at least one type each, reflecting the plant-based components of the EAT–Lancet diet. Depressive symptoms were measured using the CES-D scale, and multimorbidity was defined as the coexistence of obesity and depressive symptoms. Temporal trends were examined using χ² tests. Sex-stratified logistic regression, population attributable fraction (PAF) analyses, and joint exposure analyses were conducted with adjustment for covariates.
RESULTS:
Obesity prevalence increased (χ² for trend = 6.20, P=0.0128) and depressive symptoms rose(χ² for trend = 8.77, P=0.003) , while multimorbidity remained stable (P=0.058). Boys consistently showed higher prevalence of obesity (9.4% vs 4.0%) and multimorbidity (1.5% vs 1.0%), whereas girls had higher depressive symptoms (22.0% vs 17.1%; all P<0.001), with a widening sex gap over time. High weekend PA and adherence to PHDI-green were all associated with significantly lower odds of overweight among both sexes (all P<0.001). Both moderate and high weekend PA showed stronger protective associations with depressive symptoms in girls (all P for sex difference<0.001), whereas PHDI-green adherence was more strongly associated with reduced depressive symptoms in boys (boys: OR = 0.63, 95% CI 0.61-0.65; girls: OR = 0.66, 95% CI 0.64-0.68; P for sex difference<0.001). For multimorbidity, higher weekly PA, moderate-to-high weekend PA and PHDI-green adherence were protective in both sexes (all P<0.001). PAF analyses identified low weekend PA as the leading attributable risk factor among girls (obesity 10.2%, depressive symptoms 31.3%, multimorbidity 35.6%), whereas non-adherence to PHDI-green was most important among boys (obesity 7.0%, depressive symptoms 23.8%, multimorbidity 21.9%). Joint analyses showed the lowest risk of all outcomes among adolescents with high weekend PA and PHDI-green adherence, particularly for multimorbidity (boys: OR = 0.40, 95% CI: 0.34-0.46; girls: OR = 0.33, 95% CI: 0.26-0.43).
CONCLUSION:
Weekend PA emerged as a critical window for health promotion, particularly among girls, while PHDI-green adherence played a more prominent protective role among boys. These findings support sex-sensitive, time-targeted lifestyle interventions to improve adolescent health.